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    <meta charset="UTF-8">
    <title>03-attr()【了解】</title>
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        a[href^="http"]::after {
            content: "[ "attr(href) " ]";
        }
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<body>
    <a href="http://www.baidu.com">百度</a><br>
    <a href="http://www.jd.com">京东</a><br>
    <a href="http://www.taobao.com">淘宝</a>
    <a href="#">呵呵</a>
    <a>哈哈</a>
</body>

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